One of the valuable commodities for a well operator is time. The faster downhole operations can be accomplished, the more the operator saves. Prior procedures for milling a window in a casing have involved the placement, orientation, and securing of a whipstock. In the past this has involved many steps. Traditionally, a packer was run in the hole and set. This packer had an anchor slot for a whipstock anchor. After the packer was set, measurement of the orientation of its anchor slot had to be determined, generally in a separate trip into the well. Having determined the orientation of the anchor receptacle in the packer, the whipstock was run-in with generally a starter mill and secured to the packer. Once the whipstock was secured, the starter mill would be engaged to start the milling of the window. The starter mill would then be removed from the wellbore and a window mill inserted on a different trip to complete the cutting out of the window in the casing.
Subsequently, a one-trip milling system for a window was developed and is fully described in the Jurgens U.S. Pat. No. 5,109,924. This system eliminated an extra trip to replace the starter mill with a window mill. The combination of mills preassembled to a whipstock, as illustrated in the Jurgens patent, allowed the milling of the window from start to finish after the whipstock was properly oriented and supported.
Prior designs have attempted to combine the packer and whipstock for insertion into the wellbore in a single trip. These have generally involved hydraulically set packers that have required the use of jumper hoses around the whipstock to access the packer. These prior techniques of combining the packer and whipstock, using fluids diverted through the bottomhole assembly, had various mechanical and operational difficulties, generally involving difficulty in running the assembly into the well and reliability of the assembly once the proper depth was reached. One example of this technique is the A-Z International Casing Sidetrack System. This system has generally been used with a starter mill, which still necessitated an extra trip for switching out the starter mill to a window mill.
Thus, an objective of this invention is to provide for a truly one-trip system that allows the proper placement and orientation of a whipstock and packer assembly, coupled with a design which is simple and reliable to use and operate. The overall bottomhole assembly, using the technique of the Jurgens patent, is truly a one-trip system in that the whole bottomhole assembly is run in the wellbore, followed by setting the packer where it secures the whipstock support, followed by drilling the entire window, all without coming out of the hole a single time.
Other advantages are to create a positive barrier downhole to meet with normal offshore safety procedures by providing a packer design to go with the whipstock which will reliably give such positive sealing. Another objective is to design the packer to actuate off of applied pressure in the wellbore so as to permit the use of a large piston to ensure a good packoff and to take advantage of hydrostatic pressures to continually boost the sealing pressure on the packer assembly. Another object is to make the design simple enough for it to be function-checked at the surface before being run in the hole. Those and other advantages will become more apparent from a review of the description of the preferred embodiment.